Cellular responses to a variety of extracellular signals are typically mediated by intracellular signaling pathways, and dysregulation of such pathways, especially those involved in cell growth and differentiation, is considered to be the main cause of cancer. Ras proteins, including H-RAS, N-RAS, and K-RAS, play key roles in signal transduction, and mutations in RAS proto-oncogenes are estimated to be implicated in about 20% to 30% of all human tumors. The highest rate of RAS mutations are found in adenocarcinomas of the pancreas (90%), the colon (50%), and the lung (30%), as well as in follicular and undifferentiated carcinomas of the thyroid (50%). RAS mutations are also found in hematologic malignancies, including acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), and juvenile myelomonocytic leukemia (JMML) (Reuter et al., Blood 2000;96: 1655-1669).
Reversible tyrosyl phosphorylation represents a major regulatory mechanism to orchestrate cellular responses to external stimuli, including cell proliferation, survival and differentiation. Tyrosyl phosphorylation levels are modulated by the antagonistic actions of protein tyrosine kinases and protein tyrosine phosphatases, and are frequently deregulated in cancer. PTPN11 is a cytoplasmic Src homology-2 (SH2) domain-containing protein tyrosine phosphatase that plays a key-role in intracellular signaling elicited by a number of growth factors, hormones and cytokines (Neel, et al., Trends Biochem Sci. 2003;28:284-293; Tartaglia et al., Nat Genet. 2001;29: 465-468). The accumulated data provide evidence that PTPN11 positively modulates the signal flow in most circumstances, even though it can also function as negative regulator depending upon its binding partner and interactions with downstream signaling networks. Specifically, PTPN11 positively controls RAS function, and is required for the activation of the mitogen-activated protein kinase (MAPK) cascade induced by several growth factors and cytokines (Maroun et al., Mol Cell Biol. 2000;20:8513-8525; Shi et al., Mol Cell Biol. 2000;20:1526-1536; Yu et al., Oncogene 2003;22:5995-6004). In contrast to the structurally related SHP-1, which is expressed primarily in hematopoietic cells, PTPN11 (“SHP-2”) is widely expressed in both embryonic and adult tissues, and is required in several developmental processes, including hematopoiesis (Tang et al., Cell 1995;80:473-483; Qu et al., Mol Cell Biol. 1997;17:5499-5507; Saxton et al., EMBO J. 1997;16:2352-2364; Qu et al., Mol Cell Biol. 1998;18:6075-82; Saxton et al., Nat Genet. 2000;24:420-423; Chen et al., Nat Genet. 2000;24:296-9; Qu et al., Blood 2001;97: 911-914; Chan et al., Blood 2003;102: 2074-80).
JMML, formerly termed chronic myeloid leukemia or chronic myelomonocytic leukemia, is a myeloproliferative/myelo-dysplastic disorder of childhood characterized by excessive proliferation of immature and mature myelomonocytic cells that originate from a pluripotent stem cell (Emanuel P D, et al., Mol Med Today 1996; 2:468-475; Arico M., et al., Blood 1997; 90:479-488). In childhood, JMML accounts for approximately 30% of cases of myelodysplastic (MDS) and myeloproliferative (MPS) syndromes and 2% of leukemia's (Hasle H, et al., Leukemia 1999;13:376-385). JMML typically presents in infancy and early childhood, and is often lethal (Niemeyer C M, et al., Blood 1997; 89:3534-43; Luna-Fineman S, et al., Blood 1999;15:93459-466). Chromosomal abnormalities are observed in approximately 35% of cases, with monosomy of chromosome 7 being the most prevalent aberration. The distinctive characteristic of JMML in vitro is the “spontaneous” proliferation of leukemic cells that are hypersensitive to granulocyte-macrophage colony stimulating factor (GM-CSF) (Emanuel P D, et al., Blood 1991;77:925-929).
Approximately 15-30% of JMML cases are believed to result from oncogenic RAS mutations that specifically affect GTP hydrolysis, leading to the accumulation of RAS in the GTP-bound active conformation (Kalra R, et al., Blood 1994;84:3435-9; Miyauchi J, et al., Blood 1994;83:2248-54; Side L E, et al., Blood 1998;92:267-72; Flotho C, et al., Leukemia 1999; 13:32-7). In addition, JMML has been reported in children with neurofibromatosis type 1 (NF1), an autosomal dominant disorder resulting from germ line loss-of-function mutations of the NF1 tumor suppressor gene (Niemeyer C M, et al., Blood 1997;89:3534-43). In children with NF1 and JMML, the proliferative advantage of the leukemic cells resulting from a second hit, the somatic loss or inactivation of the normal NF1 allele (Shannon K M, et al., N Engl J Med 1994;330:597-601; Side L, et al., N Engl J Med 1997;336:1713-20). Since the NF1 gene product, neurofibromin, is a negative modulator of RAS function, this loss is associated with RAS hyperactivity (Bollag G, et al., Nat Genet 1996;12:144-8) and appears to be restricted to GM-CSF signaling in hematopoietic cells in vivo (Birnbaum R A, et al., Mol Cell 2000;5:189-95). There is also strong evidence that hypersensitivity to GM-CSF, due to a selective inability to down-regulate the RAS-MAPK cascade, plays a central role in the clonal cell growth characteristics of JMML (Birnbaum R A, et al., Mol Cell 2000;5:189-95; Iverson P O, et al., Blood 2002;99;4147-53). Nevertheless, mutations in NRAS, KRAS2, or NF1 account only for about 40% of JMML cases (Kalra R, et al., Blood 1994;84:3435-9; Miyauchi J, et al., Blood 1994;83:2248-54; Side L E, et al., Blood 1998;92:267-72; Flotho C, et al., Leukemia 1999;13:32-7).
Acute leukemia is the most common malignancy among children and adolescents, and groups a number of biologically diverse clonal disorders of hematopoietic stem cells (Greaves M., Eur J Cancer. 1999;35:1941-1953). Among these malignancies, acute lymphoblastic leukemia (ALL) accounts for 75-85 percent of cases, with precursor B-cell ALL being the most prevalent condition. Although remarkable progress has been made in the treatment of childhood ALL (Pui et al., Rev Clin Exp Hematol. 2002;6: 161-180), the underlying molecular events resulting in malignant transformation still remain poorly understood. Gene rearrangements and other chromosomal abnormalities are common, with prevalence of individual rearrangements depending on age, cell lineage and differentiation stage (Greaves M., Eur J Cancer. 1999;35:1941-1953; Harrison C J, Foroni L., Rev Clin Exp Hematol. 2002;6:91-113). Mutations affecting tumor-suppressor genes and oncogenes have also been documented, at initial presentation or during relapse (Luibbert et al., Blood 1990;75:1163-1169; Felix et al., J Clin Invest. 1992;89:640-647; Drexler H G., Leukemia 1998; 12:845-59), and genetic susceptibility associated with deficiency or low activity of enzymes that detoxify carcinogens have been reported (Krajinovic et al., Blood 1999;93:1496-1501; Wiemels et al., Proc Natl Acad Sci USA. 2001;98:4004-4009). Nevertheless, in a relatively large percentage of cases, malignant transformation does not appear to be associated with any known molecular lesion.
The respective prevalences of JMML, ALL, and acute myeloid leukemia (AML) are increased in Noonan syndrome (NS), an autosomal dominant disorder characterized by short stature, facial dysmorphia, skeletal defects, congenital cardiac defects, and hematological anomalies (Noonan, Am. J. Dis. Child. 1968,116:373-380; Allanson, J. Med. Genet. 1987;24:9-13). NS is a relatively common syndrome with an estimated incidence of 1:1000 to 1:2500 live births. It was recently demonstrated that germ-line mutations in PTPN11, the gene encoding the ubiquitously expressed protein tyrosine phosphatase PTPN11 or SHP-2, is associated with about 50% of NS cases (Tartaglia et al., Nat Genet 2001; 29:465-68; Tartaglia et al., Am J Hum Genet 2002; 70:1555-63). PTPN11 is involved in the regulation of the MAPK kinase pathway parallel to or upstream of Ras (Cunnick J M, et al., Journ. Biol. Chem. 2002;277:9498-9504; O'Reilly et al., Cell Res 2000; 10:279-288). Methods of diagnosing and treating NS based on perturbation of PTPN11 activity or signaling, are described in co-pending application Ser. No. 10/262,552, filed Oct. 1, 2002, claiming priority from provisional application 60/326,532, filed Oct. 1, 2001, each of which is hereby incorporated by reference in its entirety.
While a number of therapeutic or surgical treatments are available for leukemia and other cancers, the elucidation of the molecular events ultimately responsible for the development and progression of the disease will allow for the design of drugs and treatments strategies that more specifically target the aberrant mechanism or component. The development of specific diagnostic, preventive, and therapeutic methods, however, continue to depend on the identification and characterization of specific disease targets. The present invention addresses these and other needs in the art.